Coordination of an SVC with a ULTC reserving compensation margin for emergency control

This paper proposes a coordinated control scheme of an SVC (static VAr compensator) and a ULTC (under load tap changer) of a distribution substation to obtain a larger operating margin of SVC for emergency control. The conventional method can cause a lack of operating margin of SVCs in some conditions. It, however, is important to secure an operating margin for emergencies. In the proposed coordinated control system, SVC controls the voltage and ULTC responds to the SVC compensation value based on the relation between SVC compensation and ULTC tap position. In order to reserve the operating margin of the SVC, the time delay of ULTC is adaptively changed according to the operating condition of the SVC. Numerical simulations verify that the proposed system could increase the operating margin of SVC while improving the quality of load voltage.